Implantable medical devices (IMD) may provide a variety of different therapies and other functions including stimulation, drug infusion, physiological sensing, and the like. The IMDs receive programming from an external device and may also share information that has been collected with the external device. Many IMDs communicate with the external device using an inductive form of telemetry where a telemetry head is held in communication range of the IMD so that inductive signals may be exchanged.
The inductive downlink is obtained by a coil within the IMD that is tuned to a telemetry frequency, e.g., 175 kilohertz, being emitted by a coil within the external device. Likewise, the inductive uplink is provided by a coil within the IMD that is tuned to emit signals at a telemetry frequency of the coil of the external device. The uplink and downlink telemetry frequencies are frequently the same and a single coil in each device is tuned to a single frequency that is used for both the uplink and the downlink.
Many IMDs operate on battery power and therefore have a limited lifetime of operation before a replacement or a recharge is necessary. For IMDs with a rechargeable power source, the recharge energy may be received via inductive coupling. The external device has a coil tuned to a recharge frequency, e.g., 5 kilohertz, which may differ from the telemetry frequency. Many commercially available IMDs have a second coil that is tuned to the recharge frequency being emitted by the external device. However, the circuitry utilizing the first and second coils may be distinct circuits that may share only power and ground connections, may require more pads and ultimately more space on a circuit board, and so forth.
Furthermore, while using two coils of distinct circuits within the IMD adequately establishes telemetry and recharge applications, the size occupied by two separate coils of distinct circuits restricts the ability to make smaller IMDs. Thus, miniaturized IMD designs may call for a reduction in the space being occupied by the two coils. In some cases the miniaturized designs may call for a single coil such that the inclusion of the telemetry application of one circuit having a telemetry coil precludes inclusion of the recharge application of a distinct circuit having a recharge coil.